Download Cardiovascular System: Blood Vessels and Circulation

Chapter 13
 Vessels
carry blood to peripheral tissues,
and the nature of the exchange that
occurs between the blood and interstitial
fluids.
• form a closed tube that carries blood away from
the heart, to the cells, and back again.

Vessels consist of: arteries, arterioles,
capillaries, venules, and veins
 Blood
coming from the heart to the
capillaries travel through the arteries and
arterioles.
 Arteries are strong, elastic vessels
adapted for carrying high-pressure
blood.
 Arteries become smaller as they
divide and give rise to arterioles.
 The
wall of an artery and vein consist of
an endothelium(tunica interna) tunica
media (smooth muscle), and tunica
externa (connective tissue).
 Arteries are capable of vasoconstriction
as directed by the sympathetic
impulses; when impulses are inhibited,
vasodilation results.
 An artery has a thicker wall and small lumen
than a vein.
Comparison of a Artery and
Vein
 Only
blood vessels whose wall permit
exchange between the blood and
surrounding interstitial fluid.
 Capillaries are the smallest vessels,
consisting only of a layer of endothelium
through which substances are exchanged
with tissue cells.
 Areas with a great deal of metabolic activity
(leg muscles, for example) have higher
densities of capillaries.
 Capillaries
do not function as individual
unites but as part of a interconnected
network called a capillary bed.
 Blood entering capillaries contains high
concentrations of oxygen and nutrients
that diffuse out of the capillary wall and
into the tissues.
Capilla
ry Bed
 Hydrostatic
pressure drives the passage
of fluids and very small molecules out of
the capillary at this point.
 At the venule end, osmosis, due to the
osmotic pressure of the blood, causes
much of the tissue fluid to return to the
bloodstream.
 Venules
leading from capillaries merge
to form veins that return blood to the
heart.
 Veins have relatively thin walls because
they do not need to withstand much
pressure.
 Veins have the same three layers as
arteries have and have a flap-like valve
inside to prevent backflow of blood.
 Pressure
and resistance both affect blood
flow to tissues, but they have opposing
effects.
 Blood flow and pressure are directly
related: when pressure increases, flow
increases.
 Blood flow and resistance are inversely
related: when resistance increases, flow
decreases.
 When
a pressure difference exists, a
liquid will flow from an area of higher
pressure toward an area of lower
pressure.
 Flow rate is directly proportional to this:
the greater the difference in pressure, the
faster the flow.
 Largest pressure difference is found
between the base of the aorta and
entrance to the right atrium.
 Resistance
is any force that opposes
movement. In the cardiovascular system,
it opposes the movement of blood.
 The circulatory pressure much be great
enough to over the total peripheral
resistance.
 Greatest pressure difference occurs in
the arterial network
 Blood
pressure is the force of blood
against the inner walls of blood vessels
anywhere in the cardiovascular system,
although the term "blood pressure"
usually refers to arterial pressure.
 Arterial
blood pressure rises and falls
following a pattern established by the
cardiac cycle.
 During ventricular contraction, arterial
pressure is at its highest (systolic
pressure).
 When ventricles are relaxing, arterial
pressure is at its lowest (diastolic
pressure).
 Blood
pressure is measured by using a
sphygmomanometer.
 An inflatable cuff is placed around the
arm, when inflated the cuff squeezes the
brachial artery. A stethoscope is placed
over the artery.
 A tube connects the cuff to a pressure
gauge that measure the pressure inside
the cuff.
 Air is slowly let out of the cuff.
 When
the pressure in the cuff falls below
systolic pressure, blood can enter the
artery again.
 First, blood enters at peak systolic blood
pressure and then continues to fall below
diastolic blood pressure, where blood
flow become continuous
 Read as “120/80”
Systolic
Pressure
Diastolic
Pressure
 Cardiovascular
regulation is to ensure
that blood flow changes occur at the
appropriate time, right area, and with
drastically altering blood pressure and
blood flow to organs.
 Controlled by Autoregulation and Neural
and Endocrine mechanisms.
 Changes
in tissue conditions act directly on
precapillary sphincters to alter peripheral
resistance, producing changes in the
pattern of blood flow.
 Factors that promote the dialation of
precapillary sphincters are called
vasodilators.
 Factors that stimulate the constriction of
precapillary sphincters are called
vasoconstrictors.
 Cardiovascular
centers detect changes in
tissue demand by monitoring arterial
blood, especially blood pressure, pH, and
gas concentration.
 Baroreceptor reflexes- monitor changes
in blood pressure
 Chemoreceptor reflexes- respond to
changes in chemical composition.
 The
endocrine system provides shortterm regulation of cardiac output and
peripheral resistance with epinephrine
and norepinephrine from the adrenal
medullae.
 Hormones involved in long-term
regulation of blood pressure and volume
are antidiuretic hormone (ADH) and
angiotensinII, erythropoietin(EPO) and
atrial naturetic peptide(ANP)
 ADH
and angiotensinII promote
peripheral vasoconstriction.
 ADH and aldosterone promote water and
electrolyte retention and stimulate thirst.
 EPO stimulates red blood cell production
 ANP encourages sodium loss, fluid loss ,
reduces blood pressure, inhibits thirst,
and lowers peripheral resistance.
 Shock
is an acute circulatory crisis
marked by low blood pressure and
inadequate blood flow.
 Causes of shock: Fall in cardiac output
after fluid loss, damage to the heart,
external pressure on the heart, or
extensive peripheral vasodialation
 Caused
by a reduction of about 30% of
total blood volume.
 Symptoms: -pale, cool, moist skin
-confusion, disorientation
-rise in heart rate
-stop in urination
-drop in blood pH
 When
blood volume declines by more than
35%, homeostatic mechanisms become
unable to cope with the situation
 Low blood pressure and low venous return
lead to decreased cardiac output and
myocardial damage, reducing cardiac
output.
 Carotid sinus baroreceptors trigger a
massive activation of sympathetic
vasoconstrictors
 Which
reduces blood flow to peripheral
tissues in order to maintain adequate
blood flow to the brain.
 Must receive immediate treatment to
help eliminate fatal consequences.